Dehydrogenating hydrocarbons is an important commercial hydrocarbon conversion process because of the great demand for dehydrogenated hydrocarbons for the manufacture of various chemical products such as detergents, high octane motor fuels, pharmaceutical products, plastics, synthetic rubbers, polymerization monomers and other products well known to those skilled in the art. Processes for the dehydrogenation of light acyclic hydrocarbons are well known to those skilled in the hydrocarbon conversion arts. For instance, the dehydrogenation of C.sub.2 -C.sub.5 paraffins is well known. Because the light paraffins are relatively volatile, a more complicated separation scheme and a bulk condensation is normally required to effect the separation of the product olefins from the light by-products and hydrogen which are simultaneously produced in the process. It is therefore believed that U.S. Pat. No. 4,381,418 (Gewartowski et al) is pertinent for its teaching of a catalytic dehydrogenation process for C.sub.2.sup.+ normally gaseous paraffinic hydrocarbons and the recovery of the products of the reaction. U.S. Pat. Nos. 4,430,517 and 4,486,547 issued to Imai et al and U.S. Pat. No. 4,469,811 issued to Lucien are believed pertinent for their teaching of catalysts and operating conditions which can be employed for the dehydrogenation of low molecular weight paraffins.
Pressure swing adsorption (PSA) provides an efficient and economical means for separating a multi-component gas stream containing at least two gases having different adsorption characteristics. The more-strongly adsorbable gas can be an impurity which is removed from the less-strongly adsorbable gas which is taken off as product; or, the more-strongly adsorbable gas can be the desired product, which is separated from the less-strongly adsorbable gas. For example, it may be desirable to remove carbon monoxide and light hydrocarbons from a hydrogen-containing feed stream to produce a purified (99.sup.+ %) hydrogen stream for a hydrocracking or other catalytic process where these impurities could adversely affect the catalyst or the reaction. On the other hand, it may be desirable to recover more-strongly adsorbable gases, such as ethylene, from a feed to produce an ethylene-rich product.
In pressure swing adsorption, a multi-component gas is typically fed to at least one of a plurality of adsorption beds at an elevated pressure effective to adsorb at least one component, while at least one other component substantially passes through. At a defined time, feed to the adsorber is terminated and the bed is depressurized by one or more co-current to the direction of feed depressurization steps wherein pressure is reduced to a level which permits the separated, less-strongly adsorbed component or components remaining in the bed to be drawn off without significant removal of the more strongly adsorbed components. Then, the bed is depressurized by a countercurrent depressurization step wherein the pressure on the bed is further reduced by withdrawing desorbed gas countercurrently to the direction of feed. Finally, the bed is purged and repressurized.
Those skilled in the art of hydrocarbon processing, more particularly the dehydrogenation of hydrocarbons, are constantly searching for ways to recover a liquid product from a dehydrogenation zone in the most convenient and economical manner.